1. Field of the Invention
This invention relates to an optical pick-up apparatus adapted to access different types of disks.
2. Description of the Related Art
An optical disc such as CD(Compact disc) and CD-R(CD-Recordable) is used to write audio, video and digital text information and so on, as a recording medium. The optical disc are used to record large amounts of information. To this end, there has recently appeared a DVD(Digital Versatile Disc) capable of recording amounts of information comparable to the CD and CD-R. A DVD is not only higher than the CD and CD-R in track density, but also the distance extending from the disc surface to the recording layer is less than previous disks. For example, the distance between the disc surface and the recording layer in a DVD is 0.6 mm while that in a CD and CD-R is 1.2 mm. Also, the recording layer of a DVD has characteristics different from that of the CD and CD-R. Due to the structural differences between a DVD and a CD and CD-R, the DVD demands an optical pick-up apparatus different from the optical pick-up apparatus for a CD and CD-R. The optical pick-up apparatus for a DVD cannot access a CD and CD-R because of the aberration of the light beam. Aberration of the light beam is generated between the surface and recording layer of a CD and CD-R due to the larger distance between the surface and recording layer than the distance in a DVD. Also, the aberration of the light beam appears on the optical pickup apparatus for a CD and CD-R as the difference between the wave lengths of the light beams.
FIG. 1 shows an optical pick-up apparatus of an infinite optical system having a flux diameter controller to remove such aberrations when a CD and CD-R are accessed. The optical pick-up apparatus includes a first hologram module 12, a beam splitter 14, a collimator 16 and a reflective mirror 18 aligned in a horizontal direction. Also, the optical pick-up apparatus of FIG. 1 also includes a second hologram module 20 located at the beam splitter 14, a flux diameter controller 22 and an objective lens arranged between the reflective mirror 18 and a disc 10A or 10B. The first and second hologram modules 12 and 20 each have a light source and a photo detector. The light source of first hologram module 12 generates a light beam having a wavelength of 650 nm to be irradiated on the DVD 10A, while the light source of the second hologram module 20 irradiates another light beam having a wavelength of 780 nm on the CD or CD-R 10B. The beam splitter 14 transmits the light beams from the first and second hologram modules 12 and 20 to the collimator 16, and allows the light beams from the collimator 16 to be distributed to both the first and second hologram modules 12 and 20. The collimator 16 causes the light beams from the beam splitter 14 to proceed toward the reflective mirror 18 in parallel. The flux diameter controller 22 controls the flux diameter of a light beam transmitted between the reflective mirror 18 and the objective lens 24, according to the disc 10A or 10B. If DVD 10A is accessed, i.e., when the light beam has the wavelength of 650 nm, the flux diameter controller 22 allows the light beam from the reflective mirror 18 to go directly toward the objective lens 24. On the other hand when accessing CD/CD-R 10B, the flux diameter controller 22 decreases the flux diameter of the light beam from the reflective mirror 18 and transmits the light beam having a decreased flux diameter to the objective lens 24. The objective lens 24 converges the light beam from the flux diameter controller 22 onto the recording layer of the disc 10A or 10B, i.e., on the recording layer of the DVD 10A or on the recording layer of the CD or CD-R 10B, in the shape of a spot. Light beams having a wavelength of 650 nm are irradiated on the recording layer of DVD 10A in the shape of a spot, while light beams having a wavelength of 780 nm are irradiated on the recording layer of the CD or CD-R 10B in the shape of a spot.
In the optical pick-up apparatus of FIG. 1, since the flux diameter controller 22 is located between the collimator 18 and the objective lens 24, the configuration is complex and the manufacturing costs are great. Also, a light beam can only be traced to a track on the disc 10A or 10B if the flux diameter controller 22 an objective lens 24 are driven by actuator 26. The heavy weight load of the actuator limits the speed at which the disc may be access to a critical speed. Furthermore, in the optical pick-up apparatus of FIG. 1, each of the first and second hologram modules 12 and 20 must be accurately installed at the demanded location such that the center axis of the light beam proceeding from the first hologram module 12 is united with the center axis of the light beam proceeding from the second hologram module 20. However, the center axis of the light beam proceeding from the first hologram module 12 can not be united with the center axis of the light beam proceeding from the second hologram module 20 due to a locating error and an angle error caused in the combination of the optical pick-up apparatus.
Accordingly, it is an object of the present invention to provide an optical pick-up apparatus which can adaptively compensate for the aberration of the light beam according to the type of disk.
It is another object of the present invention to provide an optical pick-up apparatus which has the facility to unite center axes of light beams from two light sources.
In order to obtain said objects of the invention, according to one aspect of the present invention, an optical pick-up apparatus comprises: a first light source for generating a first light beam having a first wavelength to be irradiated on a disk; a second light source for generating a second light beam having a second wavelength to be irradiated on the disk; and a light path for irradiating the first light beam from the first light source on the disk in the shape of a spot by a finite optical system and the second light beam from the second light source on the disk in the shape of a spot by an infinite optical system.
Further, according to other aspect of the present invention, an optical pick-up apparatus comprises: a first light source for generating a first light beam having a first wavelength to be irradiated on a disk; a second light source for generating a second light beam having a second wavelength to be irradiated on the disk; an objective lens for irradiating the first and second light beams from the first and second light sources on the disk in a shape of spot; a beam splitter for guiding the first light beam from the first light source and the second light beam from the second light source to the objective lens; and light axis control means between the first light source and the beam splitter to remove the center axis of the first light beam.
Furthermore, according to another aspect of the present invention, an optical pick-up apparatus comprises: a first light source for generating a first light beam of a first wavelength to be irradiated on a disk; a second light source for generating a second light beam of a second wavelength to be irradiated on the disk, the second including a light element for generating the second light beam and a location controller for controlling the location of the light element in the planer; and a light path for irradiating the first light beam from the first light source and the second light beam from the second light source on the disk in the shape of a spot.